I also think linear phase is overrated....
We have to see everything in it's perspective. Only a loudspeaker with 1 driver hase a linear phase,

Except concentric (coaxial) drivers like Tannoy, TAD, Cabasse, Beyma or Altec Lansing. Not to forget the APPOLITO 's configuration.
But, at this time no digital delays where available to recover the physical delay due to the non horizontal alignment of the coils. Nowadays, we can correct this in a nice way.
We have to notice this delay problem is important at the crossover. This argue (once more) in favor to 2way horns systems, where the crossover is at low frequency (<1000Hz) , so, phase correlation will not change a lot with vertical misalignment, because the wave length is 0.34m.

Except concentric (coaxial) drivers like Tannoy, TAD, Cabasse, Beyma or Altec Lansing. Not to forget the APPOLITO 's configuration.
But, at this time no digital delays where available to recover the physical delay due to the non horizontal alignment of the coils. Nowadays, we can correct this in a nice way.
We have to notice this delay problem is important at the crossover. This argue (once more) in favor to 2way horns systems, where the crossover is at low frequency (<1000Hz) , so, phase correlation will not change a lot with vertical misalignment, because the wave length is 0.34m.

Of coarse coaxial drivers have lesser problems, I owned several Tannoy's. But most of the time they also need time alignment because their high drivers are not in the same acoustical centerpoint of the woofer due their construction.

But you can also overcome this vertical misaligment by using steeper slopes, the higher the order of the filter the smaller the frequency band where problems occur. I think using 48db filters has more effect than chasing the Fir filter holy grail.

What would be the benefit of using asymmetrical slopes for time alignment of drivers vs. a delay on the tweeter? I can see the downside (bad phase tracking) but not the upside..

Taking inspiration from the Grimm Audio LS1 I would (am) use(ing) FIR only for phase EQ and IIR filters for the crossovers. Resulting in a linear phase sytem. (rePhase and a miniDSP openDRC are my weapons of choice for phase EQ at the moment, combined with Hypex PSC2.400d based IIR XO).

Just trying to understand why you make such a choice.

Edit: (Big) typo

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Music is art - Audio is psychoacoustics & engineering

What would be the benefit of using asymmetrical slopes for time alignment of drivers vs. a delay on the tweeter? I can see the downside (bad phase tracking) but not the upside..

Taking inspiration from the Grimm Audio LS1 I would (am) use(ing) FIR only for phase EQ and IIR filters for the crossovers. Resulting in a linear phase sytem. (rePhase and a miniDSP openDRC are my weapons of choice for phase EQ at the moment, combined with Hypex PSC2.400d based IIR XO).

Just trying to understand why you make such a choice.

Edit: (Big) typo

I do not use asymmetrical slopes, it is mentioned in the article. What I want to point out is the fact that even if you use a phase linear xover, the problems with vertical misallignment still exists and is clearly shown in the polar plot. A lot of people make the mistake that if you use a linear xover, you will get a phase linear system. Well you can actually, but only in one listening position and you will need to strap your head to a headrest!

I do not use asymmetrical slopes, it is mentioned in the article. What I want to point out is the fact that even if you use a phase linear xover, the problems with vertical misallignment still exists and is clearly shown in the polar plot. A lot of people make the mistake that if you use a linear xover, you will get a phase linear system. Well you can actually, but only in one listening position and you will need to strap your head to a headrest!

Yupz, you`re quite right, all the usual design parameters have to be taken in account, time alignment being 1 of them, dispersion / lobing is another big one. The phase EQ (making the system linear phase) is just the icing on the cake.

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Music is art - Audio is psychoacoustics & engineering

Most of the time, the loudspeaker adds its own slope to the one of the filter. Not in the same way on the basses and trebles units. So, searching for symmetrical acoustical slopes drive-you most of the time to asymmetrical electronic/electric slopes.
You want to use bass speaker in the range where it does not fractionate. By habit, you will see a peak of its response curve just where you will cut-it. So your filter will have to cancel-it. No rules: each driver need a dedicated filter for the same cut-off slope.

Most of the time, the loudspeaker adds its own slope to the one of the filter. Not in the same way on the basses and trebles units. So, searching for symmetrical acoustical slopes drive-you most of the time to asymmetrical electronic/electric slopes.
You want to use bass speaker in the range where it does not fractionate. By habit, you will see a peak of its response curve just where you will cut-it. So your filter will have to cancel-it. No rules: each driver need a dedicated filter for the same cut-off slope.

In principle this is true, but with the current DSP's it's not difficult to first EQ the driver flat well beyond the XO points and apply an XO after that. This solves the problem you descibe here .

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Music is art - Audio is psychoacoustics & engineering